Omit native multi-agent guidance when native tools are disabled (#59732)

## Why

Multi-agent V2 still supplied native tool usage guidance when native tools were disabled, leaving instructions for unavailable tools in model requests.

## What changed

Skip bundled and model catalog role guidance for both root agents and subagents when `disable_native_tools` is enabled. Preserve explicitly configured usage hints.

## Testing

Add coverage for omitted bundled and catalog guidance and preserved configured hints with native tools disabled. Update the request snapshot and assert that spawned agents do not receive native tool call guidance.

GitOrigin-RevId: 6f2facabc95e78cbf64af19636a4daf488bbcc51

codex-rs/core/src/config/config_tests.rs

@@ -12893,8 +12893,11 @@ max_concurrent_threads_per_session = 17
     assert!(usage_hints.root.is_none() && usage_hints.subagent.is_none());
 }
 
-#[test]
-fn multi_agent_v2_model_override_exposure_preserves_configured_usage_hints() {
+#[test_case::test_case(false; "native_tools")]
+#[test_case::test_case(true; "native_tools_disabled")]
+fn multi_agent_v2_model_override_exposure_preserves_configured_usage_hints(
+    disable_native_tools: bool,
+) {
     let config_toml = toml::from_str(
         r###"[features.multi_agent_v2]
 enabled = true
@@ -12905,7 +12908,8 @@ expose_spawn_agent_model_overrides = true
     )
     .expect("multi-agent v2 config should parse");
 
-    let config = resolve_multi_agent_v2_config(&config_toml);
+    let mut config = resolve_multi_agent_v2_config(&config_toml);
+    config.disable_native_tools = disable_native_tools;
     assert!(config.expose_spawn_agent_model_overrides);
     assert_eq!(
         config.root_agent_usage_hint_text.as_deref(),
@@ -12933,6 +12937,23 @@ expose_spawn_agent_model_overrides = true
     );
 }
 
+#[test]
+fn multi_agent_v2_disabled_native_tools_omit_default_roles() {
+    let mut config = resolve_multi_agent_v2_config(&ConfigToml::default());
+    config.disable_native_tools = true;
+    let mut messages = ResolvedModelMessages::bundled().multi_agent();
+    for catalog_override in [false, true] {
+        if catalog_override {
+            messages.root = ResolvedMessage::Catalog("Catalog root base.");
+            messages.subagent = ResolvedMessage::Catalog("Catalog subagent base.");
+        }
+        let usage_hints = resolve_usage_hints(
+            &config, messages, /*omit_update_plan_instructions*/ false,
+        );
+        assert_eq!((usage_hints.root, usage_hints.subagent), (None, None));
+    }
+}
+
 #[test]
 fn multi_agent_v2_exposes_model_overrides_by_default() {
     let config_toml =

codex-rs/core/src/session/multi_agents.rs

@@ -52,6 +52,9 @@ pub(crate) fn resolve_usage_hints(
         if base.is_empty() {
             return None;
         }
+        if config.disable_native_tools {
+            return None;
+        }
         Some(MultiAgentRoleInstructions::Composed {
             base: base.to_owned(),
             marked: message.catalog_override().is_some(),

codex-rs/core/tests/suite/scenarios.rs

@@ -2215,7 +2215,7 @@ async fn multi_agent_catalog_parameters(disable_native_tools: bool) -> Result<()
     let (name, description) = if disable_native_tools {
         (
             "multi_agent_native_tools_hidden",
-            "Native tools are unavailable while the V2 runtime and its instructions remain enabled.",
+            "Native tools and native usage guidance are unavailable.",
         )
     } else {
         (

codex-rs/core/tests/suite/scenarios_reserved_spawn.rs

@@ -300,6 +300,7 @@ async fn same_manager_creation_preserves_live_bindings_and_attachments(
     ));
     let child_request = child_request.single_request();
     assert!(child_request.body_contains_text(UPDATED_RULE));
+    assert!(!child_request.body_contains_text("only as direct tool calls"));
     assert_eq!(
         child_request.body_contains_text(parent_message),
         fork_history

codex-rs/core/tests/suite/snapshots/all__suite__scenarios__multi_agent_native_tools_hidden.snap

@@ -2,7 +2,7 @@
 source: core/tests/suite/scenarios.rs
 expression: "context_snapshot::format_request_history_snapshot(description,\n&mock.requests(),\n&ContextSnapshotOptions::default().include_request_settings(),)"
 ---
-Scenario: Native tools are unavailable while the V2 runtime and its instructions remain enabled.
+Scenario: Native tools and native usage guidance are unavailable.
 
 ## Window 1
 Settings:
@@ -64,26 +64,8 @@ Settings:
         Never use the `request_user_input` tool for permission requests or permission-related escalations.
         </collaboration_mode>
 03:message/developer:
-    <multi_agent_role>You are `/root`, the primary agent in a team of agents collaborating to fulfill the user's goals.
-
-    At the start of your turn, you are the active agent.
-    You can spawn sub-agents to handle subtasks, and those sub-agents can spawn their own sub-agents.
-    All agents in the team, including the agents that you can assign tasks to, are equally intelligent and capable, and have access to the same set of tools.
-
-    You can use `spawn_agent` to create a new agent, `followup_task` to give an existing agent a new task an...message to a running agent without triggering a turn. [hash=7d40ff8b58977202]
-    `send_message` calls may be read by a human, so ensure they are legible. Always put proper spaces between words and/or numbers.
-    <OMITTED 17 LINES; ~246 TOKENS; hash=780031e2df907944>
-    - All agents use the same current working directory.
-    - As a result, edits made by one agent are immediately visible to all other agents.
-
-    When calling `wait_agent`, prefer longer waits (minutes) to avoid busy polling.
-
-    There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
-
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
-04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
-05:message/user:
+04:message/user:
     <environment_context>
       <cwd><CWD></cwd>
       <shell><HOST_SHELL></shell>
@@ -91,9 +73,9 @@ Settings:
       <timezone><HOST_TIMEZONE></timezone>
       <filesystem><workspace_roots><root><CWD></root></workspace_roots><permission_profile type="disabled"><...e="unrestricted" /></permission_profile></filesystem> [hash=d40b2f45cb028888]
     </environment_context>
-06:message/user:
+05:message/user:
     Check which agents are working under /root before delegating more work.
-07:configuration_update:reasoning={"effort":"low"}
+06:configuration_update:reasoning={"effort":"low"}
 -- request 2 (turn) --
-08:function_call/collaboration.list_agents:{"path_prefix":"/root"}
-09:function_call_output:unsupported call: collaborationlist_agents
+07:function_call/collaboration.list_agents:{"path_prefix":"/root"}
+08:function_call_output:unsupported call: collaborationlist_agents